WO1999065038A1

WO1999065038A1 - Simplified method of modifying a surface of a material

Info

Publication number: WO1999065038A1
Application number: PCT/US1999/013209
Authority: WO
Inventors: Regan W. Stinnett; D. C. Mcintyre; M. T. Crawford; Thomas R. Lockner; K. E. Boucher; Eugene L. Neau
Original assignee: Quantum Manufacturing Technologies, Inc.
Priority date: 1998-06-10
Filing date: 1999-06-10
Publication date: 1999-12-16
Also published as: AU5204099A; JP2002518587A

Abstract

The ability to modify a surface region of a material is significantly enhanced by irradiating the surface with a pulsed ion beam having a predetermined pulse repetition of rate, pulse width and deposited energy.

Description

SIMPLIFIED METHOD OF MODIFYING A SURFACE OF A MATERIAL

Technical Field

The present invention relates to methods for modifying a surface region of a material. The present invention is applicable to a wide variety of materials and utilizes an ion beam extracted from a magnetically-confined anode plasma (MAP) ion source having a predetermined pulse repetition rate, predetermined pulse width and a predetermined deposited energy to modify the surface region.

Background Art

The escalating requirements for enhanced performance of materials has caused an increased demand for improving the properties of materials through surface modification. One approach to surface modification is to cause the surface of a material to undergo very rapid heating and cooling thereby changing the composition of a surface and/or the relative spatial arrangement of materials on the surface. Such an approach can, in turn, significantly alter the mechanical, chemical, electrical, optical, and other properties of the surface. However, a historic barrier to widespread commercial use of rapid thermal processing, particularly when the process must exceed at least the melting point of the materials, has been the lack of a commercially viable technique for consistently treating large batches of parts or large areas.

One possible approach to thermally altering materials comprises the use of lasers. However, the use of lasers is attendant with several disadvantages. The efficiency of coupling laser energy into surfaces is strongly dependent on the optical properties of the surface being treated. Therefore, the use of lasers can result in non-uniform treatment due to defects and non-uniformities in surfaces. Also, lasers are limited because they use small beam spots (typically much less than a few square centimeters) which must be swept across a surface to treat large areas which can lead to undesirable mechanical and electrical edge effects in the treated surface. These edge effects arise because material previously treated by the laser beam is retreated by the passage of the laser beam in an adjacent area. Pulsed electron beams can also be used to modify surfaces by thermally cycling them. Pulsed electron beams raise certain issues with respect to beam transport and penetration depth in materials. Another attempted approach for thermally altering the surface characteristics of a material comprises the use of pulsed ion beams. There are, however, significant issues attendant upon the use of conventional pulsed ion beam methodology. Like lasers, use of conventional ion beams generate a high cost per unit area treated. Further, ion beam generators using "flashover" (i.e. surface-arc -based plasma sources tends to create debris that contaminates the surface being treated. Moreover, "flashover" can negatively affect the uniformity, and therefore reproducibility, and efficiency of the beam.

There exists a need for cost effective, simplified methodologies in technology enabling the modification of surface characteristics by thermally altering the surface characteristics of a material with ion beams.

Summary of the Invention

An objective of the present invention is to provide a method of modifying a surface of a material wherein the depth of the surface or near surface to be treated can be controlled and the material melted or significantly heated can be limited to a depth of only a few microns or less.

Another objective of the present invention is to provide a method of modifying a surface of a material whereby rapid cooling of the material may be obtained, especially where the targeted depth of treatment is small, enabling large areas to be treated efficiently with relatively low energies and high process rates.

According to the present invention, the foregoing and other objects are achieved in part by a method of modifying a surface of a material, the method comprising the steps of: irradiating the surface with a pulsed ion beam extracted from a magnetically-confined anode plasma (MAP) ion source with substantially no rotation, said pulsed ion beam having a predetermined pulse repetition rate of at least 0.1 pulse/second and a predetermined pulse width in a range of from about 20 nanoseconds to about 0.05 milliseconds; and depositing an energy on said surface, said energy having a predetermined energy density in a range of from about 0.01 J/cm² to about 20 J/cm².

Additional objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein embodiments of the invention are described simply by way of illustrating of the best mode contemplated in carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive.

Brief Description of Drawings

Figure 1 illustrates the use of intense ion beam pulses to rapidly thermally cycle materials according to an embodiment of the present invention.

Figure 2A-B illustrate voltage and current density waveforms according to an embodiment of the present invention.

Figure 2C illustrates thermal cycling produced in 1042 carbon steel using an energy level of 2.4 J/cm² and the waveform shapes according to an embodiment of the present invention.

Figure 2D illustrates thermal cycling produced in 1042 carbon steel using different energy levels and waveform shapes according to an embodiment of the present invention.

Figure 3A is a micrograph showing an untreated copper surface.

Figure 3B is a micrograph showing a modified copper surface after treatment.

Figure 3C is a micrograph showing a modified copper surface according to an embodiment of the present invention.

Figure 4 is a graph plotting temperature as a function of depth showing vaporization of a zinc layer while the titanium layer over it remains below its vapor temperature.

Figure 5 is a graph plotting temperature as a function of depth showing vaporization of a subsurface layer before the outer surface layer reaches its vaporization temperature.

Figure 6A shows a 17-4PH surface with high gradients in height.

Figure 6B shows a similar 17-4PH surface after treatment, illustrating a smoother surface with reduced gradients.

Figures 7A-D are micrographs illustrating modified surfaces according to an embodiment of the present invention.

Figures 8A-B are micrographs depicting cemented tungsten carbide surfaces before and after treatment according to an embodiment of the present invention.

Figures 9A-C are micrographs depicting alumina/A 1 surfaces before and after treatment according to embodiments of the present invention.

Figure 10A is a micrograph depicting 303 stainless steel treated according to an embodiment of the present invention.

Figure 1 OB is a micrograph depicting 304 stainless steel treated according to an embodiment of the present invention.

Figure 11 is a graph plotting temperature as a function of depth in 304 stainless steel.

Detailed Description of the Invention Ion Beam Source

In accordance with embodiments of the present invention, a surface of a material can be modified by irradiating the surface with an ion beam extracted from a ion magnetically- confined anode p (MAP) source having a predetermined pulse repetition rate of at least 0.1 pulses/second, a predetermined pulse width in a range of about 20 nanoseconds to about 0.05 milliseconds; and depositing an energy on the surface, the energy having a predetermined deposited energy in a range of from about 0.01 J/cm² to about 20 J/cm²

The ion beam source utilized to practice the methods of the present invention is an ion beam source which provides a magnetically confined or guided anode p source, such as the (MAP) ion beam system. MAP ion beam systems are described in U.S. Patent Nos. 5,473,165, 5,525,805, 5,532,495, 5,656,819 and 5,900,443, the disclosures of which are incorporated herein by reference in their entireties. In accordance with embodiments of the present invention, the ion beam is a repetitive extractable ion beam having a repetition rate of at least about 0.5 pulses/second. Provision of such pulses can be accomplished without significant beam system damage or debris production.

In accordance with embodiments of the present invention, the ion beam is extracted with substantially no rotation from an ion source. As used herein, the term "substantially no rotation" means that the annular ion beam extracted from the beam system has an azimuthal rotational velocity that is less than 30% of the axial velocity toward the target after passing through all of the magnetic fields in the beam system, i.e. a ratio of rotational velocity to axial velocity of less than 0.3. In accordance with embodiments of the present invention, the ion beam can have a ion species composition of, for example protons or nitrogen and a species purity of 60% or greater, and the beam can have a deposited energy density level greater than 0.01 Joules/cm², such as, for example, from about 0.1 J/cm² to about 20 J/cm². In the present invention, the p position can be determined by the magnetic field profile rather than material surfaces. In other words, the location of the source ions being accelerated by the accelerating electric field between the anode and the cathode in the beam system, is primarily determined by the shape and magnitude of guiding magnetic fields in the beam system rather than by solid surfaces directly.

In one embodiment of the present invention, contamination is at least partially cleaned by irradiating a region of the surface with an ion beam having the requisite parameters. As used herein, "contamination" is intended to include the presence in the surface region of any unwanted material. As used herein, "cleaning" is intended to include changing the structure and chemical state of a surface by preferentially removing the contaminant from the surface or by altering the distribution of the contaminant on the surface of a material.

Altering the arrangement of atoms in a surface, the composition of the surface, and the topography of a surface can also affect the properties of a coating or similar layer subsequently applied to the surface. For example, vaporization of impurities combined with sealing of cracks and pores and smoothing can be expected to improve the adhesion and inherent properties of a layer applied to the surface by techniques such as sputtering or evaporation. As used herein, the term "surface" means both the nominal, two-dimensional surface/ plane of a material and includes the near surface e.g., to a depth of about 300 micrometers. Contaminants which can be cleaned from surfaces by the present invention include, by way of example only, an iron surface contaminated by a hydrocarbon, a metal surface contaminated with an oxide, a cemented carbide surface contaminated with tin or titanium nitride, and a ceramic surface contaminated by a metal. In one embodiment, the contaminated surface cleaned by vaporizing the contaminant by raising the surface to a temperature greater than the vaporization point of the contaminant and less than a vaporization point of the surface material.

Thus, contaminated surfaces can be cleaned by removing unwanted low vapor point contaminants on their surface by raising the temperature on the surface above the vapor point of the contaminant without vaporizing other surface components. This cleaning can be accomplished without the use of conventional cleaning solvents. Referring now to Figure 2C, essentially any contaminant with a vapor point lower than the vapor point of the surface material can be removed by the present methods. For example, hydrocarbon contaminants typically have vapor points below 1000°C whereas iron has a melting point of 1576°C. Thus, an iron surface contaminated with hydrocarbons can be cleaned by irradiating the surface with an ion beam to raise the surface to a temperature greater than the vaporization point of the hydrocarbon but less than the melting point or vaporization point of the iron surface. That is, the hydrocarbon contaminant can be removed without melting and resolidification of the iron surface. Cleaning can also be achieved by vaporization of the contaminant and melting of the iron surface. Vaporization of the contaminant can also promote mixing of the contaminant with the surface material. In another embodiment, the contaminant and surface material are at least partially mixed by raising the temperature of the surface material to a temperature sufficient to melt the contaminant and the surface material, thereby cleaning the surface. By melting two or more of the components of the surface material and allowing them to at least partially mix together, as by liquid phase mixing, convective, diffusive or other mixing processes at elevated temperatures, a new state of the surface results, thereby mitigating deleterious effects of one of the mixed materials. For example, both iron (melting point of 1576°C) and chromium (vapor point of 2665°C) can be melted and mixed when they are raised above 2000°C. In this case, both iron and chromium will be melted and undergo mixing, as by liquid phase and possibly, convective mixing, without vaporization of either constituent so long as the surface temperature remains below the vapor point of the iron and the chromium.

In another embodiment, a surface is at least partially cleaned by irradiating the surface with an ion beam to raise the temperature of the surface to at least the melting point of at least one of the materials of the surface but not the contaminant. Melting material in the vicinity of a contaminant can allow the contaminant to be mixed into the material by convective, and/or diffusive, and/or other diffusion mechanisms. As an example, if particles with a high melting point temperature (temperature A) are located on the surface of a material, at least part of which contains a lower melting point temperature material temperature B), the particles may be at least partially mixed into the lower melting point material if the ion beam raises the temperature of the surface above temperature B but below temperature A. Contaminants such as matter from the dust, inclusion, or second phase particle material may be melted and then trapped in solid solution by rapid cooling following termination of the beam heating.

In another embodiment, a contaminated surface can be cleaned by irradiating the surface with an ion beam to raise the surface to a temperature sufficient to melt the contaminant and the surface material but which is also greater than the vaporization point of one of the surface material and the contaminant to remove the contaminant and/or also potentially promote at least partial mixing of the surface material and the contaminant.

The removal of contamination can play a critical role in altering several characteristics of the surface. For example, the removal of an oxide from a surface can increase both the surface electrical conductivity and the optical reflectance of the material. Metal oxides tend to exhibit low electrical conductivity and also tend to cause the surface to appear dull. Pulsed ion beam treatment parameters can be chosen such that the oxide is removed by vaporization of the oxide. The resulting surface essentially free of oxide, typically appear brighter and will usually have a higher electrical conductivity.

In a further embodiment of the present invention, a zone in a contaminated surface is refined by inducing the contaminant to migrate toward an outer boundary of the surface. Thereafter, the migrated contaminants can be removed from the surface.

In zone refining, contaminants having different properties, such as melting point, than the rest of the surface material are swept along a resolidification front that forms as the surface material resolidifies at the deepest melt depth in the irradiated material and proceeds toward the surface. This results in the accumulation of contaminants on the surface. Once on the surface, these contaminants can be removed by vaporization or other processes. However, even if contaminants are not subsequently removed from the surface, the underlying material is purified of the contaminants.

In a further embodiment of the present invention, a layer, such as a coating, can be separated and/or removed from a surface by irradiating the layered surface with an ion beam. In one embodiment, the layer to be separated and/or removed may itself comprise multiple layers.

Separation and/or removal of a layer can be accomplished by, for example, delamination due to volume expansion and contraction of the surface, causing stresses that result in cracking and mechanical separation and other phenomena associated with stress waves induced by the thermal cycling. Thermal cycling can be accomplished by heating and/or melting the surface underlying the layer to be removed. Alternatively, separation and/or removal of layers can be achieved by vaporizing a surface material below a given layer, thereby creating pressure between that layer and the underlying surface material to force separation of the layer from an underlying surface. For example, an incident ion beam can deposit energy in a multi-layer coating such that a zinc layer below a titanium outer layer reaches its vapor point while the titanium outer layer remains in the solid or liquid phase. The pressure caused by vaporization of the underlying zinc vapor layer would cause the titanium outer layer to separate and/or move away from the zinc surface, thus effectively removing the titanium layer. Referring to Figure 4, about one micron of a zinc layer is vaporized while a one micron thick titanium layer over it remains below its vapor temperature. When vaporization first occurs at a point below the surface, not only can an overlying layer be removed, but a new surface is also provided for subsequent use that has been melted and homogenized. This is shown in Figure 5, which illustrates vaporization of a subsurface layer before the outer surface layer reaches its vaporization temperature.

In another embodiment of the present invention, a crystalline surface is modified by irradiating the surface with an ion beam having a predetermined pulse repetition rate, a predetermine pulse width and a predetermined deposited energy to heat the surface, and permitting the surface to cool at a rate sufficient to substantially alter the grained surface. As used herein, "crystalline surface" generally refers to a surface that contains at least some areas where that atoms or molecules are in a regular spatial pattern, a crystalline arrangement or similar surface characteristic. As used herein, the term "altering the "crystalline surface" is generally intended to mean altering the regular spatial pattern, crystalline arrangement or other surface characteristics of the atoms or molecules and/or the sizes of the areas over which the regular spatial arrangement of atoms or molecules exists.

According to embodiments of the present invention, rapid melt and resolidification, as where cooling after melt is faster than a million degrees Centigrade/second, dramatically reduces grain size. The melted surface can be made either nanocrystaline (grain size much less than one micron) or amorphous (no grains). This can be achieved by the use of short ion beam pulses, such as pulses of 150 ns in duration. Referring to Figure 2c, cooling rates of greater than 10⁸-10⁹ K s can be achieved in steel. Grain refinement provides an improved surface for subsequent coating. For example, grain refinement can provide a tougher and sometimes harder surface that will enhance the performance of the coating under mechanical stress.

In another embodiment of the present invention, a surface containing cracks and/or pores or other low density features may be modified by irradiating the surface with a pulsed ion beam having the prerequisite parameters to substantially reduce and/or eliminate the cracks or pores or other low density features in the surface. As used herein "low density features" include any feature that contains less material than the areas immediately adjacent to the feature.

Low density features like cracks and pores can be reduced and/or eliminated by melting the surface such that liquid flows into the low density features to close the features before the surface resolidifies. The reduction or elimination of low density features is also an important benefit in preparing surfaces for coatings. For example, cracks in the surface being coated can create defects in the coating uniformity and can also provide sites of mechanical stress that can cause failure of the coating by cracking the coating. Cracks can also allow contaminants to collect. Subsequent coatings deposited on this contaminated location can have poor adhesion to the surface due to the presence of the contaminants.

Densification of a surface and removal of surface-connected porosity improves the effectiveness of other materials modification processes. For instance, the presence of surface connected porosity can reduce the effectiveness of hot isostatic pressing or other pressurized densification processes. Surface-connected pores provide a pathway for pressure equalization between the interior and exterior of a part, reducing the ability of the pressurized media to density the part. Surface sealing of pores allows there to be a pressure differential and thus densification of the part. Another associated benefit of sealing pores is the improvement of corrosion resistance of the surface by preventing trapping or penetration of corrosive agents from the exterior of the part into the interior of the part.

Densification of a surface and removal of cracks can also increase the fatigue lifetime of the material. Cracks are well known to be potential sites for cracks that can propagate or become longer in a fatigue environment. Propagation of such defects can eventually lead to part failure by fracture or plastic deformation. Elimination or reduction in the number and/or size of such features by ion beam treatment can lead to an increase in the fatigue lifetime of the material.

Densification of surface characterized by large cracks or pores or other low density features can be improved by the combination of irradiating with a pulsed ion beam and a pre- treatment "shot peening" or similar technique that serves to reduce the size of the cracks or pores so that the melting and flowing of material in the liquid phase of processing is able to more completely and easily seal the resulting surface.

In yet another embodiment of the present invention, the topography or spatial gradient of a surface is altered by irradiating the surface with an ion beam having a predetermined pulse repetition rate, a predetermined pulse width and a predetermined deposited energy. As used herein, the term "topography" means the configuration of a surface including its relief and the position of its features. The term "spatial gradient" means the rate of change in the relative position of adjacent features or materials on the surface.

Thermal cycling, such as melting and vaporization, of a surface can alter the topographical characteristics of a surface in a variety of ways, including roughening, smoothing, and/or texturing the surface. Embodiments of the present invention include raising the temperature of the surface above the melting point of at least one of the materials on the surface, raising the temperature of the surface to a point below the vaporization point of the surface, raising the temperature of the surface without substantially removing surface material, and raising the temperature of the surface to a point above the vaporization point of at least one of the materials on the surface. For example, catalyst surfaces can be modified to achieve increased surface area, and finer grain structure. Surface topography and microstructure changes can be achieved by rapid melting and resolidification, vaporization, and/or vaporization and recondensation of catalyst material on the pre-existing surface. These changes can improve the activity of the catalyst.

A surface can be at least partially flattened to reduce the spatial gradient by smoothing the surface to substantially reduce and/or eliminate projections above the nominal surface thereof. Projections, such as burrs, can be substantially reduced and/or eliminated. Multiple melt and resolidification cycles can be used to reduce or eliminate burrs or surface structures much larger than the melt depth. Also, vaporization can reduce and/or eliminate projections. Projections above the nominal surface of a material cause non-uniformity in subsequently applied coatings and also cause applied coatings to crack when the relatively mechanically weak, coated projecting structure is detached, for example by contact with another surface in a wear situation. The present methodology permits flattening without removing surface material, thus preserving the overall dimensions of the treated surface.

The present invention is also applicable to smooth a surface to substantially reduce and/or eliminate depressions below the nominal surface thereof. As used herein, the term "depressions" means an area that is recessed from the nominal average position of the surface. By removing or partially smoothing depressions, especially those with high spatial gradients, as by filling in pits, the adherence of a subsequently applied coating will be enhanced. This is because pits in the surface can lead to stress concentration, coating defects or non-uniformity, and early failure by cracking and delamination of coatings. This reduction of stress concentration, reduction of surface gradients and improvement of surface quality extends the lifetime of uncoated surfaces. Figure 6 illustrates a surface treated according to the methodology of the present invention where the distinctiveness/high spatial gradient of the projections and depressions of a surface have been reduced.

The smoothing of the topography can also have a significant effect on the friction properties and optical properties of a surface. Smoother surfaces can present a surface with lower friction when in sliding or moving contact with an adjacent surface. Also, it is well known that a smoother surface will provide for increased reflected light and increase specular reflection of light.

The present invention is also applicable to roughen a surface. As used herein, the term "roughen" means to create or increase the size of projections above the nominal surface. Examples of such projections include sharp tips. One advantage of the present methodology is that a surface can be roughened without removing material, as shown in Figures 3B and 3C and Figure 6. Roughening may result from a combination of effects including volume change from thermal cycling, three dimensional effects, non-uniform heat flow, and surface tension during resolidification. An example of a wave-like structure/topology produced on copper is shown in Figure 3b.

The extent of change of the topography can be adjusted by adjusting the melt depth during processing. Reducing the melt depth can produce a smoother surface. The melt depth can be adjusted by reducing or increasing the energy deposited in the surface. Lower deposited energy results in reduced melt depth as shown in Figure 2C and 2D. The effect of volume expansion can be minimized by pre-heating the material to be treated. This reduces the localized change in temperature upon cooling between the surface layer and the underlying, untreated material that is not affected significantly by the thermal cycling produced by the ion beam.

In one embodiment, the temperature of the surface is raised to a point above the vaporization point of at least one of the materials in the surface to effect surface roughening. Rapid vaporization of surfaces can produce stress waves in the material by the reaction force produced by the heated material leaving the surface with a velocity characterized by its temperature or other energy state. In some cases the material surface may already be in the liquid phase. If the stress wave encounters the surface while it is still molten, material can be ejected from the surface by splashing. The surface features due to splashing can be frozen in by rapid resolidification. By rapidly vaporizing surface material during multiple pulses, recondensation of vaporized material on the surface can produce very rough surfaces of rapidly resolidified, fine grain or amorphous material in states achieved by rapid quenching from the vapor or liquid phases.

Depending on the initial structure of the surface, the redeposition can produce sharp tips . Depending on the material, the incident beam energy and the number of pulses, these structures can be grown to extend well above the original surface. Such a surface is shown in Figure 7 (formed using several hundred pulses at energy levels of 4-8 Joules per square centimeter). Alternatively, Figure 3c shows a surface comprising bumps and tips formed using 2-4 Joules per square centimeter for 40 pulses. These roughened surfaces structures provide many advantages including their ability to be used as field enhanced points for emission when electric fields are applied. An example of surface roughening in which vaporization is important is shown in Figure 3c. As shown in Figure 7, repeated ablation of the surface can also produce sharp tips on the surface.

Surface roughening provides several advantages including increasing the exposed surface area, providing more sites for mechanical interlocking for subsequently applied layers, creating different surface topographies for more or less friction. This provides controllable lubricity, and creation of points whose topography result in enhancement of electric fields around them to facilitate field-induced emission from the points. This surface preparation capability can be important for both bare surfaces and coated surfaces. When the surface is being prepared for subsequent coatings, a rougher surface can provide more surface area for bonding of the coating and better mechanical interlocking of the coating to the surface. For both uncoated and coated surfaces, the roughened or textured surface can provide locations for lubricants to collect and provide enhanced lubricating capability for a longer duration during use.

Surface texturing can also change the electronic and chemical properties of a surface. When the present invention is used to make a surface smoother, the reduction in the population of electric field enhancing features can improve the ability of a surface to withstand the presence of high electric fields without emitting electrons. Also, reducing the roughness of a surface reduces the amount of material exposed to corrosive agents. On the other hand, roughening a surface can increase the tendency of a surface to emit electrons in the presence of an electric field and increase the chemical reactivity of a surface by increasing the surface area.

Surface texturing, either smoothing and roughening, can also change the optical properties of surfaces, making them less reflective, less specular and more diffuse if the surface is rougher, and making them more reflective, more specular, and less diffuse when the surfaces are smoother. In particular, processing at levels above the melt temperature (typically in the energy range of 2-10 J/cm²) can make surfaces shiny and more reflective.

In another embodiment of the present invention, a surface is raised to a temperature below the melting point of the surface by irradiating the surface with an ion beam having the requisite parameters The surface can comprises one or more separate components which may be present as layers, partial layers, or separate, intermixed regions or islands.

The treatment of any material, including mixed materials by thermal cycling at temperatures below the melting point of any of the constituents can produce dislocations leading to increased hardness and compressive stress, and other effects resulting from the thermally induced expansion and contraction of the material, especially of mixed materials with different thermal expansion coefficients. Heating below the melting point can also cause solid state rearrangement of the atoms by means of crystallographic phase change or other solid state process which in turn, can change mechanical, electrical, chemical, and other properties of the treated material.

In another embodiment of the present invention, a surface comprising at least two components is modified by raising the surface to a temperature above the melting point of at least one component. The treatment of a mixed material by thermal cycling at temperatures above the melting point of at least one of the components can produce a variety of beneficial effects including, for example, reduced grain size of the melted material, increased microstructural defects in the melted material, partial dissolution of higher melting point material into the melted material, and changes in the properties of the melted material (such as by solutionizing, reprecipitating or similar effects). Reprecipitating some of the partially dissolved, higher melting point material would be one specific example of this effect.

Referring to Figure 8, a cemented tungsten carbide material with 6% cobalt binder was treated at 2 J/cm² according to an embodiment of the present invention. This treatment resulted in melting of the Co binder without melting of the WC particles. In cutting tests, this treatment produced a 60% lifetime extension of cemented tungsten carbide tools used for cutting cast aluminum alloy. This may be due to a combination of effects resulting from melting the Co binder without melting the WC particles, including grain refinement of the Co, partial dissolution of the WC into the binder, and possibly reprecipitation of solutionized constituents upon cooling or subsequent post-treatment heating of the material.

In another embodiment of the present invention, a surface is modified by providing a surface comprising a first component having a first melting point, applying a second component having a second melting point to the surface, wherein the first melting point is lower than the second melting point, and raising the surface to a temperature greater than or equal to the first melting point and below the second melting point.

This method can be used to incorporate other materials into a surface, including those with higher melting points than the original surface. For example, fine particles with dimensions up to several times the range of the ions in the beam, can be incorporated into a surface by melting the surface and either fully melting, partially melting, or even heating only of the particle, resulting in at least partial bonding of the particles to the surface. This approach can be used to mix ceramics into metals or metals into ceramics thereby altering the electronic properties of the surface. By way of example only, metals can be mixed into the surface of insulators or semiconductors to reduce the electronic breakdown voltage and at the same time increase the average electronic emissivity of the surface. By extending this effect to multiple pulses it is possible to partially or fully incorporate the material of the particle into the surface, resulting in an alloyed surface. By repeatedly adding new particles or material, this effect can be used to build up new material on the surface up to any desired depth. Deposited coatings can also be incorporated into the surface material using this technique.

Treatment of mixed materials with different melting points can also be used to create new materials. For example, ion beams can be used to melt mixed powders of different melting point materials to produce either melt-bonded, or partially or fully alloyed materials by using the ion beam to melt at least one of the constituents of the powder mixture. One embodiment of this technique is the melting of mixed powder material. By repeatedly adding new powder and creating bonded material by melting at least one constituent of the mixed powder, it is possible to create new alloyed layers of any desired depth. These layers can also be bonded to underlying or overlaid materials by melting the interface between them.

In another embodiment of the present invention, a layered surface is at least partially mixed by irradiating the interface between the layer and the surface with an ion beam having the requisite parameters. The difference in melting points between adjacent layers can be used to mix and/or bond layers by melting an underlying layer with lower melting temperature, with or without melting the upper layer. The interface between the layer and the surface can be wholly or partially mixed. Even when complete mixing and homogenization of the interface is not achieved, partial mixing of the interface results in graded interfaces without distinct boundaries with high spatial gradients, which, when otherwise present are a preferred site for cracking and other mechanical failure, galvanic corrosion, and other deleterious effects.

In yet another embodiment of the present invention, a surface comprising a precipitate is modified by reprecipitating the surface. Specifically, the surface is irradiated with a pulsed ion beam having a selected accelerating voltage, ratio of rotational velocity to axial velocity, pulse width, ion species composition, and deposited energy level.

By way of example, 17-4PH stainless steel was hardened by the present methodology. Specifically, untreated stainless steel had a measured Knoop (100 g load) hardness of 414. After treatment, the hardness decreased to 282. This was probably because the treatment resulted in dissolving the pre-existing precipitates that were present to increase the hardness of precipitation hardened materials. After post-treatment heating/tempering at 500°C for two hours, the hardness increased to 530. This increase in hardness may be due to the reprecipitation of finer grain precipitates than were originally present, leading to increased hardness. The present invention is also applicable to thermally cycle the near surface region of materials to produce dislocations. Such cycling produces stress waves that result in dislocations in the material, especially metals. These dislocations result in increased hardness and in residual compressive stress that can be beneficial in many applications. The use of the present methodologies to achieve this enables treatment of surfaces to enhance lifetimes by reducing fatigue problems and wear.

The methodology of the present invention can achieve separation of mixed materials without affecting the underlying material by removing at least one component of the mixed material. This can be achieved by selective vaporization and/or dissociation. Many materials, including cermets, composites, intermetallics, alloys, and similar substances, are composed of mixtures of different constituents than respond differently to thermal cycling. These materials can be separated by selective vaporization or dissociation based on the difference in vapor and melt points of the different constituents.

Figure 9 (Al/Al₂O₃ treatment) illustrate how the present invention separates such mixed materials. Figure 9 shows the separation of aluminum from an aluminum/alumina mixture, leaving a rough surface due to the effects of the aluminum vaporization. By choosing the incident ion beam species, energy, and intensity, the temperature of the treated material can be selected to cause vaporization of the lower vapor point constituents while not vaporizing the higher vapor point materials. This effect can be used to transform surfaces without affecting the underlying material. This is useful as where the transformed material is a coating on a substrate and it is desired that the substrate should remain substantially unchanged by the process.

In another embodiment, the present invention relates to modifying a surface comprising a first and a second component by raising the surface to a temperature sufficient to at least partially remove the first component.

The removal of the lower vapor point constituent(s) can produce altered topography. Figures 10a and 10b demonstrate the treatment of two stainless steel surfaces with different sulfur (a low vapor point material-440°C) contents. The sulfur may be present in the alloy as free sulfur or in combination with another element to form a sulfide. In Figure 10a and 10b, respectively, the surface was 303 and 304 stainless steel. Both surfaces were treated using approximately 2.5 Joules per square centimeter. The thermal cycling due to this treatment is shown in Figure 11. The rough surface produced on the 303 material illustrated the vaporization of low vapor point material present in the 303 material due to its higher sulfur content. The sulfur content of the 304 material is much lower so the treated surface was much smoother.

The production of rough or textures surfaces by vaporization or dissociation can produces surfaces with different visual appearance, different friction coefficients and lubricity, different wear and fatigue characteristics, and different chemical characteristics including chemical activity rates. This effect can also be used to provide surfaces or films with different levels of porosity. In addition, rough surface structures can be produced that can be used as field enhanced points for emission when electric fields are applied. This can also be achieved using the other surface roughening techniques described herein. Dissociation of materials (e.g., TiN) that respond to thermal cycling by dissociating into its constituent elements can produce similar effects. The methods of the present invention can be used to remove dissociatable material from a surface or from a matrix of other material that does not dissociate or vaporize until higher temperatures are reached. The removal of the dissociatable constituent(s) can be used to produce the same effects described herein using vaporization.

The mixing or alloying of vaporized or dissociated material that is redeposited and mixed into the remaining material can also affect the surface properties of the surface produced.

Surfaces can also be repaired using the present invention by adding material to a portion of the surface and using the beam to melt and bond the new material to the surface. This technique can be used to repair damaged or incomplete surfaces. By melting the new material and the underlying original material, the new material will be bonded by liquid phase diffusion and, possibly, convective mixing. This results in a graded interface that resists delamination. In addition, the melting of only one of the materials results in enhanced diffusive bonding and improved adhesion of the new material. The use of a third material that melts more easily that the other materials to be bonded can also be melted, resulting in enhanced bonding of the multi-layered composite.

Embodiments of the present invention are well suited for improving surfaces formed from powder material. Powder metallurgy applications can benefit from the homogenization, cleaning, and smoothing, densification and hardening by heating and/or melting, liquid phase bonding and mixing, surface texturing and production of fine grain material that the present invention can provide as shown in the improvement of the metal injection molded part shown in Figure 6. The techniques for treating mixed materials is also well suited to use with powder material, both metals and non-metals.

The methodology of the present invention can be used to implant ions in polymer surfaces. This produces benefits such as increased hardness, reduced permeability, and increased electrical conductivity. The use of the present methodology also achieved several unique benefits in the treatment of polymer surfaces:

(1) Treatment using the short (<lms) pulses drastically reduces the time that the surface is at temperatures high enough to cause damage to the polymer. This enables faster treatment to be achieved using higher ion intensities.

(2) Treatment using short pulses also increases the acceptable peak temperature of the surface during treatment by decreasing the damage resulting from exceeding the standardly accepted maximum treatment temperature for continuous or long time scale treatment. One additional advantage of this high acceptable treatment temperature is the increased effectiveness of cross-linking that results from the higher temperatures and resultant increases mobility of the molecules during and shortly after treatment. This can reduce the ion dose needed to achieve specific hardness or other parameters resulting from treatment.

(3) The present invention provides, in a single pulse, a spectrum of ion energies and also can provide multiple ion species that results in more uniform treatment throughout the treated depth than that resulting from the monoenergetic implantation used in present, continuous beam systems.

(4) The relatively high average ion power and ion power density delivered and the resulting high throughput rates achievable using the present invention can significantly improve the economics of ion implantation relative to present ion implantation processes.

The present invention can modify the surface properties in a variety of ways including altering, such as increasing or decreasing the chemical reactivity, catalytic activity, sliding and/or fretting and/or erosion wear resistance, galvanic and/or pitting and/or crevice corrosion resistance, electron emissivity, adhesiveness for subsequently applied layers and/or coatings, sliding and/or rolling friction coefficient, rolling and/or sliding contact fatigue resistance, optical reflectance, diffuse reflectance, brightness, and compressive residual stress of the surface. In the previous description, numerous specific details are set forth, such as specific materials, structures, chemicals, processes, etc., to provide a better understanding of the present invention. However, the present invention can be practiced without resorting to the details specifically set forth. In other instances, well known processing and materials have not been described in detail in order not to unnecessarily obscure the present invention.

Only the preferred embodiment of the present invention and but a few examples of its versatility are shown and described in the present disclosure. It is to be understood that the present invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein.

Claims

What is claimed is:

1. A method of modifying a surface of a material, the method comprising the steps of: irradiating the surface with a pulsed ion beam extracted from a magnetically-confined anode plasma (MAP) ion source with substantially no rotation, said pulsed ion beam having a predetermined pulse repetition rate of at least 0.1 pulse/second and a predetermined pulse width in a range of from about 20 nanoseconds to about 0.05 milliseconds; and depositing an energy on said surface, said energy having a predetermined energy density in a range of from about 0.01 J/cm² to about 20 J/cm².

2. The method according to claim 1, wherein said step of depositing further comprises depositing energy on said surface, said energy having an energy density in a range of from about 0.1 J/cm² to about 10 J/cm².

3. The method according to claim 1, wherein the pulsed ion beam has a pulse repetition rate of at least about 0.5 pulses/second.

4. The method according to claim 1, wherein the pulsed ion beam has an ion species purity of at least 60%.

5. The method according to claim 1, wherein said pulsed ion beam modifies an area greater than 5 cm²/pulse.

6. The method according to claim 1, wherein the modification comprises cleaning and the surface includes a contaminant, and further comprising the step of partially cleaning said contaminant.

7. The method according to claim 6, wherein said step of cleaning further comprises vaporizing the contaminant by raising the surface to a temperature greater than a vaporization point of the contaminant and less than a vaporization point of the surface material.

8. The method according to claim 7, wherein the step of vaporizing further comprises promoting mixing of the contaminant with the surface material.

9. The method according to claim 6, further comprising the step of at least partially mixing the contaminant and the surface material by raising the temperature of the surface material to a temperature sufficient to melt the contaminant and at least a constituent of the surface material.

10. The method according to claim 9, wherein the step of mixing further comprises raising the surface material surface to a temperature which is greater than the vaporization point of either the surface material or the contaminant.

11. The method according to claim 1 , wherein the modification comprises refining a zone in a surface, said zone containing a contaminant and further comprising the step of inducing the contaminant to migrate toward an outward boundary of the surface.

12. The method according to claim 11, further comprising the step of at least partially cleaning the contaminated surface by removing the migrated contaminant from the surface.

13. The method according to claim 1, wherein the modification comprises separating and/or removing a layer and further comprising the step of at least partially separating and/or removing a layer from a surface.

14. The method according to claim 13, wherein the layer is adjacent the surface.

15. The method according to claim 14, further comprises the step of heating the surface adjacent the layer to be separated and/or removed.

16. The method according to claim 13, further comprising the step of melting the surface adjacent the layer to be separated and/or removed.

17. The method according to claim 13, further comprising the step of vaporizing the surface adjacent the layer to be separated and/or removed.

18. The method according to claim 1, wherein said surface includes an interface between a surface material and a layer of material adjacent said surface material, and further comprising the step of at least partially mixing the surface material and the layer material at said interface.

19. The method according to claim 1, wherein said surface is crystalline and further comprising the step of heating the crystalline surface to modify the crystalline surface.

20. The method according to claim 19, further comprising the step of converting the crystalline surface to an amorphous surface.

21. The method according to claim 20, further comprising coating the surface.

22. The method according to claim 1, wherein said surface includes low density features and further comprises the step of melting at least one material of said surface to substantially reduce said low density features in the surface.

23. The method according to claim 22, further comprising the step of coating the treated surface.

24. The method according to claim 1, wherein said surface has a spatial gradient and further comprising the step of at least partially flattening the surface to reduce the spatial gradient.

25. The method according to claim 24, wherein said step of at least partially flattening further comprises the step of at least partially melting at least one material of the surface material by raising the temperature of the surface above its melting point.

26. The method according to claim 25, wherein said step of at least partially flattening further comprises raising the temperature of a material of the surface material to a temperature below its vaporization point.

27. The method according to claim 26, wherein said step of raising the temperature is accomplished essentially without removing material from the surface.

28. The method according to claim 24, wherein said spatial gradient includes projections and wherein said step of flattening further comprises at least partially smoothing the surface by reducing projections.

29. The method according to claim 24, wherein said spatial gradient includes pits and wherein said step of flattening further comprises at least partially smoothing the surface by reducing pits.

30. The method according to claim 1, further comprising the step of roughening at least part of the surface.

31. The method according to claim 30, wherein said step of roughening comprises at least partially melting at least one component of the surface.

32. The method according to claim 31 , wherein said step of roughening comprises at least partially vaporizing at least one material of the surface by raising the temperature of the material above its vaporization point.

33. The method according to claim 30, comprising creating projections in said surface.

34. The method according to claim 30, comprising creating sharp tips in said surface.

35. The method according to claim 1, further comprising heating the surface to a temperature below its melting point.

36. The method according to claim 35, wherein the surface comprises at least two materials, and further comprising the step of raising the temperature of the surface above the melting point of at least one of the materials.

37. The method according to claim 1, wherein the surface comprises a first material having a first melting point, and further comprising the steps of applying a second material having a second melting point to the surface, wherein the first melting point is lower than the second melting point; and raising the temperature of the surface to a temperature greater than or equal to the first melting point and below the second melting point.

38. The method according to claim 1, wherein the surface comprises a first material having a first melting point, and further comprising the steps of applying a second material having a second melting point to the surface; and raising the temperature of the surface to a temperature greater than or equal to the first melting point.

39. The method according to claim 38, further comprising the step of resolidifying the surface.

40. The method according to claim 39, wherein the second material is a powder.

41. A method according to claim 1 , further comprising the step of generating a new or altered distribution of precipitates.

42. The method according to claim 40, wherein the surface material comprises at least one metal or a mixture of metals.

43. A method according to claim 1, wherein the surface comprises at least a first material and a second material, and further comprising the step of raising the temperature of the surface to a temperature sufficient to at least partially remove the first material.

44. The method according to claim 43, wherein the step of raising the temperature comprises vaporizing the first material.

45. The method according to claim 44, wherein the step of raising the temperature comprises dissociating the first material.

46. The method according to claim 1, further comprising the step of heating the modified surface.

47. The method according to claim 46, wherein the step of further comprises tempering the surface.

48. The method according to claim 46, wherein the step of heating further comprises hot isostatic pressing.